Auto merge of #61492 - RalfJung:const-qualif-comments, r=eddyb

[rust.git] / src / librustc / hir / map / definitions.rs

diff --git a/src/librustc/hir/map/definitions.rs b/src/librustc/hir/map/definitions.rs
index 3edd75fb725dafbd8fa66855c43135641019bb96..6a561f0c63a2afa556eb4563bbd33f7c414e7a7c 100644 (file)
--- a/src/librustc/hir/map/definitions.rs
+++ b/src/librustc/hir/map/definitions.rs
@@ -582,9 +582,17 @@ pub fn to_string(&self) -> String {
     }
 }
 
+/// Evaluates to the number of tokens passed to it.
+///
+/// Logarithmic counting: every one or two recursive expansions, the number of
+/// tokens to count is divided by two, instead of being reduced by one.
+/// Therefore, the recursion depth is the binary logarithm of the number of
+/// tokens to count, and the expanded tree is likewise very small.
 macro_rules! count {
-    () => (0usize);
-    ( $x:tt $($xs:tt)* ) => (1usize + count!($($xs)*));
+    ()                     => (0usize);
+    ($one:tt)              => (1usize);
+    ($($pairs:tt $_p:tt)*) => (count!($($pairs)*) << 1usize);
+    ($odd:tt $($rest:tt)*) => (count!($($rest)*) | 1usize);
 }
 
 // We define the GlobalMetaDataKind enum with this macro because we want to